Turn it off and on again: characteristics and control of torpor

Abstract

Torpor is a hypothermic, hypoactive, hypometabolic state entered into by a wide range of animals in response to environmental challenge. This review summarises the current understanding of torpor. We start by describing the characteristics of the wide-ranging physiological adaptations associated with torpor. Next follows a discussion of thermoregulation, control of food intake and energy expenditure, and the interactions of sleep and thermoregulation, with particular emphasis on how those processes pertain to torpor. We move on to take a critical view of the evidence for the systems that control torpor entry, including both the efferent circulating factors that signal the need for torpor, and the central processes that orchestrate it. Finally, we consider how the putative circuits responsible for torpor induction integrate with the established understanding of thermoregulation under non-torpid conditions and highlight important areas of uncertainty for future studies.

Mechanosensation of the heart and gut elicits hypometabolism and vigilance in mice

“…The hypometabolism and vigilance that we observed during excitation of NDG Oxtr closely resembles torpor, which is a state that heterotherms, like mice, enter when the availability of metabolic fuel is insufficient to meet real or perceived energetic demands 12 . Because torpor slows metabolic rate and alters fuel utilization, methods that artificially induce torpor have been explored for a variety of applications [39][40][41] .…”

“…Towards this end, we reveal that NDG Oxtr innervate the aortic arch and portions of the gastrointestinal tract, where they form structural endings consistent with mechanosensation. Fascinatingly, chemogenetic activation of NDG Oxtr produced a phenotype resembling torpor, which is a state of hypometabolism that heterotherms enter when exposed to energetically demanding environments 12 . Collectively, our results demonstrate that perceived mechanosensation of the heart and gut potently alters metabolism and behavior to cope with threats originating from the internal milieu.…”

The role of species ecology in predicting Toxoplasma gondii prevalence in wild and domesticated mammals globally

“…Since T . gondii can only successfully infect endothermic species, we tested if mammalian species undergoing torpor or hibernation with the accompanying decreased body temperature [ 34 ] and reduced time frame for exposure opportunities had a lower prevalence than ecologically comparable species. Finally, we evaluated how vagility could impact the prevalence of T .…”

“…Similarly, since T. gondii can be transmitted in utero, we assessed if T. gondii prevalence was higher in species with longer gestation duration, given the larger infection window for maternal-fetal transmission. Since T. gondii can only successfully infect endothermic species, we tested if mammalian species undergoing torpor or hibernation with the accompanying decreased body temperature [34] and reduced time frame for exposure opportunities had a lower prevalence than ecologically comparable species. Finally, we evaluated how vagility could impact the prevalence of T. gondii.…”